Fresh water accounts for only around 2.5% of the total water on Earth. Its distribution varies considerably, and many millions of people live in arid and semi-arid parts of the world where fresh water supplies are limited. Millions of others live in areas where inadequate water supply is compounded by water pollution associated with rapid urbanisation, industrialisation and population growth. World Health Organization (WHO) figures show that 87% of the world's population now using drinking water from safer, improved sources, but in sub-Saharan Africa this figure drops to only 60% of the population, and only 50% in Oceania. However, the WHO has been criticised for its focus on improved sources, which relates to the physical structure of the water source and not the quality of the water itself, and it is thought that the number of people without access to clean drinking water is considerably higher than the official figures suggest. The picture is bleaker for sanitation, with WHO figures stating that 39% of the world’s population live without access to improved sanitation, the vast majority of whom live in Asia and sub-Saharan Africa. The WHO estimate that 1.4 million children die from diarrhoea every year as a result of unclean water and poor sanitation.
Irrigation of agricultural crops accounts for around 70% of all freshwater withdrawals from rivers, lakes and aquifers globally. Excessive diversion of rivers for irrigation has had disastrous consequences in some areas, most famously for the Aral Sea in the former Soviet Union, which has shrunk to a fraction of its original size. Withdrawal of water from aquifers is also of serious concern, causing a fall in the water table in numerous countries, including parts of Mexico, Yemen and India. Projections suggest that the Middle East is headed for a serious water shortage at current usage rates due to its shrinking ground water reserves, particularly the depletion of its underground fossil aquifers that are not naturally refilled with rainwater. Many countries in the region rely on imported staple foods as their water reserves are too low to irrigate crops. For example, Saudi Arabia began wheat production irrigated by a fossil aquifer in the 1970s, but had to begin phasing it out in 2008 due to the resulting major decline in its water reserves. In response to increasing worries over food security, several Gulf states are now engaged in securing foreign land for agriculture. There are concerns that this land grab is taking place in many countries involved in post conflict reconstruction with poor levels of development, and water supplies may be overused to the detriment of local populations.
Climate change and fresh water
Climate change poses a significant threat to fresh water availability. Rising temperatures are likely to affect rates of evaporation, reducing the downward movement of water and diminishing the replenishment of groundwater supplies. Rainfall patterns are also likely to change, increasing the probability of extreme weather events including droughts and floods. These impacts are expected to increase the number of countries facing water scarcity, affecting access to drinking water as well as food security. Water is therefore set to become the major resource challenge for the twenty first century.